Wideband systems have recently received a great deal of interest due to their potential for high-speed wireless communication. Among the several new wireless technologies, Ultra-Wide-Band (UWB) communication is expected to be used for many consumer electronic products in the near future. A UWB system transmits an extremely low-power signal over a wide range of frequencies from 3.1 to 10.6 GHz allowing data rates as high as several hundred Mb/s. To keep this solution cost-effective, the bill of materials (BOM) must be reduced as well as the power consumption. Moreover, the advantage of combining the base-band circuitry and the RF front-end on one single chip is strongly desired. Therefore, the CMOS technology is a good candidate for achieving this goal since it also takes advantage of process shrinking to reduce the overall power consumption and cost over the generations.
A significant amount of power is consumed by filter devices which, by way of example, perform filtering with a third-order low-path filter having a cut-off frequency at e.g. 400 MHz.
FIG. 10 shows a conventional Sallen & Key filter using an operational amplifier (forward buffer with a non-unity gain) as shown in FIG. 11 and a feedback capacitor C. The feedback capacitor C introduces a zero in the transfer function which decreases the attenuation of the filter at higher frequencies, for example above 400 MHz. One method of improving the attenuation is to increase the bandwidth of the forward buffer used in the filter. This is, however, associated with an increased power consumption. The conventional Sallen & Key filters further suffer from a large demand for a silicon area and a demand for a high power supply voltage.